Inkjet methods, in which droplets of an ink composition are discharged from an ink discharge orifice, are used in many printers because of small size, low cost, and image formation being possible without contact with a recording medium. Among these inkjet methods, a piezo inkjet method, in which an ink is discharged by utilizing deformation of a piezo electric element, and a thermal inkjet method, in which droplets of an ink composition are discharged by utilizing the phenomenon of boiling of the ink composition by thermal energy, are characterized by being excellent in terms of high resolution and high speed printing properties.
In recent years, development of the use of inkjet printers has been carried out not only in the field of photographic printing and document printing for domestic use and office use but also in the field of commercial printing and industrial printing. In particular, the demand for wide format inkjet printers suitable for the printing of large-size advertisement posters that are to be affixed to shop windows or walls of buildings, etc. has been increasing rapidly. Since large-size advertisement posters are often used mainly outdoors and are required to have a long-term weather resistance, polyvinyl chloride, etc. is widely used as a substrate, and pigments having an azo skeleton (mainly yellow applications), quinacridone pigments (mainly magenta applications), copper phthalocyanine pigments (mainly cyan applications), and carbon black (mainly black applications), which are excellent in terms of weatherability (light, rain, and wind), are widely used as pigments.
Furthermore, for full color printing, an inkjet ink set comprising inks of each of the three subtractive primary colors, comprising yellow, magenta, and cyan or, with the addition of a black ink, inks of four colors has been used.
As conventional ink compositions, those described in Patent Documents 1 to 4 can be cited.